Adipaldehydic acid is a useful compound as a synthetic intermediate. Some processes of producing the acid have already been known. In one process, 2-hydroxycyclohexanone is oxidized with lead tetraacetate. In another process, cyclohexanone is oxidized at a low temperature with alkaline hydrogen peroxide. However, these processes are not so advantageous, because they need expensive chemicals and are of poor yield.
Recently, it was reported that adipaldehydic acid methyl ester and dimethyl acetal thereof are produced by oxidizing cyclohexanone with molecular oxygen in methanol in the presence of ferric chloride. However, the reaction rate is too slow in this process. Besides, the process is practically disadvantageous because a complicated operation to remove the methoxy group is inevitable in order to use the resulting product, which has a methoxy group derived from methanol, as a synthetic intermediate.
In another example, it was reported that adipaldehydic acid can be produced by oxidizing cyclohexanone with molecular oxygen in the presence of water and a copper compound (Japanese Patent Publication No. 26768/1972). However, the process of the patent is disadvantageous because the conversion of cyclohexanone and the yield of the desirable product are both not sufficiently high. And also, the reaction rate is not fast enough to conduct the reaction within an advantageously short time.